From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: llvm@lists.linux.dev, Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org,
Nathan Chancellor <nathan@kernel.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 0/2] ftrace/recordmcount: Handle object files without section symbols
Date: Tue, 16 Aug 2022 22:35:34 +0530 [thread overview]
Message-ID: <1660668823.oegvwl2214.naveen@linux.ibm.com> (raw)
In-Reply-To: <20220816100423.5ee2e17c@gandalf.local.home>
Hi Steven,
Steven Rostedt wrote:
> On Wed, 27 Apr 2022 15:01:20 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>
>> This solves a build issue on powerpc with binutils v2.36 and newer [1].
>> Since commit d1bcae833b32f1 ("ELF: Don't generate unused section
>> symbols") [2], binutils started dropping section symbols that it thought
>> were unused. Due to this, in certain scenarios, recordmcount is unable
>> to find a non-weak symbol to generate a relocation record against.
>>
>> Clang integrated assembler is also aggressive in dropping section
>> symbols [3].
>>
>> In the past, there have been various workarounds to address this. See
>> commits 55d5b7dd6451b5 ("initramfs: fix clang build failure") and
>> 6e7b64b9dd6d96 ("elfcore: fix building with clang") and a recent patch:
>> https://lore.kernel.org/linuxppc-dev/20220425174128.11455-1-naveen.n.rao@linux.vnet.ibm.com/T/#u
>>
>> Fix this issue by using the weak symbol in the relocation record. This
>> can result in duplicate locations in the mcount table if those weak
>> functions are overridden, so have ftrace skip dupicate entries.
>>
>> Objtool already follows this approach, so patch 2 updates recordmcount
>> to do the same. Patch 1 updates ftrace to skip duplicate entries.
>>
>> - Naveen
>>
>>
>> [1] https://github.com/linuxppc/issues/issues/388
>> [2] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d1bcae833b32f1
>> [3] https://github.com/ClangBuiltLinux/linux/issues/981
>>
>>
>
> There's been work to handle weak functions, but I'm not sure that work
> handled the issues here. Are these patches still needed, or was there
> another workaround to handle the problems this addressed?
I'm afraid these patches are still needed to address issues in
recordmcount.
I submitted patches to remove use of weak functions in the kexec
subsystem, but those have only enabled building ppc64le defconfig
without errors:
https://lore.kernel.org/all/20220519091237.676736-1-naveen.n.rao@linux.vnet.ibm.com/
https://lore.kernel.org/all/cover.1656659357.git.naveen.n.rao@linux.vnet.ibm.com/
The patch adding support for FTRACE_MCOUNT_MAX_OFFSET to powerpc only
helps ignore weak functions during runtime:
https://lore.kernel.org/all/20220809105425.424045-1-naveen.n.rao@linux.vnet.ibm.com/
We still see errors from recordmcount when trying to build certain
powerpc configs.
We are pursuing support for objtool, which doesn't have the same issues:
https://lore.kernel.org/all/20220808114908.240813-1-sv@linux.ibm.com/
- Naveen
prev parent reply other threads:[~2022-08-16 17:06 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-27 9:31 [PATCH 0/2] ftrace/recordmcount: Handle object files without section symbols Naveen N. Rao
2022-04-27 9:31 ` [PATCH 1/2] ftrace: Drop duplicate mcount locations Naveen N. Rao
2022-04-27 13:46 ` Steven Rostedt
2022-04-27 9:31 ` [PATCH 2/2] recordmcount: Handle sections with no non-weak symbols Naveen N. Rao
2022-04-27 13:54 ` Steven Rostedt
2022-04-28 7:45 ` Naveen N. Rao
2022-04-28 14:06 ` Steven Rostedt
2022-04-28 17:24 ` Naveen N. Rao
2022-04-28 17:31 ` Naveen N. Rao
2022-05-02 14:44 ` Christophe Leroy
2022-05-02 23:52 ` Steven Rostedt
2022-05-03 11:20 ` Christophe Leroy
2022-05-03 16:25 ` Steven Rostedt
2022-05-04 16:50 ` Christophe Leroy
2022-05-04 17:06 ` Steven Rostedt
2022-05-04 17:10 ` Christophe Leroy
2022-08-16 14:04 ` [PATCH 0/2] ftrace/recordmcount: Handle object files without section symbols Steven Rostedt
2022-08-16 17:05 ` Naveen N. Rao [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1660668823.oegvwl2214.naveen@linux.ibm.com \
--to=naveen.n.rao@linux.vnet.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=llvm@lists.linux.dev \
--cc=nathan@kernel.org \
--cc=ndesaulniers@google.com \
--cc=rostedt@goodmis.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).